FX itself is reef safe. The fluids excreted by the Flatworms when they die is NOT safe for life in your tank. This is why the directions have you suck out as many Flatworms as possible first, then use the FX, then as soon as you see the Flatworm die, you imediately use carbon and start siphoing out the dead Flatworms.
I had Flatworms, they started taking over and kill most of my Polyps. I used FX per the directions and it went well. A bit later, some survivors were popping out. Then I dosed FX again and left it in the tank for two weeks. Never seen a Flatworm again.
2x Sunburst Platys (2M, 2F) // 3x Neon Tetras (?) // 2x Cherry Barbs (1M, 1F) // 2x YoYo Loaches (?) // 1x Bushy Nose Pleco (M) // 1x Clown Pleco (?) //
-30# Live Rock
-Mixed Snails (Nassarius // Cerith // Astrea // Black Turbo // Mexican Turbo)
-8x Blue Leg Hermit Crabs // 1x Banded Serpent Star // 1x Cleaner Shrimp
-1x Royal Gramma // 1x Percula Clownfish
-2x Mushroom Leather // Metallic Green Star Polyps // Pulsing Xenia // Striped Xenia // Blue Mushroom
-Remora + Maxi-Jet 1200 // 2x Maxi-Jet 600 // Maxi-Jet 400 // Visi-Therm Deluxe 50 // Current USA Orbit 2x 40w PC